Motion sensors, including accelerometers and gyroscopes, provide measurement of movement in at least six degrees of freedom. The simplest way to do motion sensing is with a solid-state mass-spring system, creating a damped simple harmonic oscillator. The movement of the solid-state proof mass can be measured with respect to displacement, velocity, or acceleration by suitable mechanical-electrical transducers. Efforts to miniaturize linear accelerometers and gyroscopes for inertial systems are mostly concentrated around Micro-Electro-Mechanical Systems (MEMS) technology. Similarly, in terms of design, fabrication, and readout, accelerometers and gyroscopes are the current leaders in commercially successful MEMS technology. Among a variety of transduction mechanisms underlying solid-state MEMS motion sensors, the most successful types are based on capacitive transduction due to the simplicity of the sensor element itself, no need for exotic materials, low power consumption, and good stability with respect to temperature. Although capacitive transducers have a characteristic nonlinear capacitance vs. displacement response, feedback is commonly used to convert the signal to a linear output. MEMS motion sensors in combination with other sensors, such as compass, pressure sensor, and GPS, have created a consumer electronics sensing package that works as the intelligent interface for users to interact with their electronics and, further on, with external environments, and have reasonable performance with low cost CMOS-compatible silicon microfabrication technology. However, in addition to high-volume consumer electronics markets requiring low-to-medium performance motion sensors, there are huge markets for high-performance motion sensing devices, with applications designed for military inertial navigation/guidance, high-resolution seismic sensing, and high-g sensors. The key requirements for these high-performance applications include small size, wide bandwidth, low noise floor, low cross-axis sensitivity, low drift, wide dynamic range, high shock survivability, and low power consumption. There has been plenty of work done along the direction of scaling down the device size while maintaining low noise, high sensitivity and high resolution using MEMS techniques. However, the design and fabrication of these solid-state MEMS devices are complicated, which can result in low reliability, low reproducibility, and high cost. More importantly, they have yet to prove satisfactory for specific applications, especially in low frequency seismic sensing, because of the inherent limitation of the working mechanism of the solid-state mass-spring system. For some applications they also have limited successes due to their fragility to high shocks.
In contrast to a device having a solid inertial mass, a molecular electronic transducer (MET) utilizes a liquid electrolyte relative to fixed electrodes to sensitively measure movement. METs are part of a third class of fundamental electronic devices, characterized by charge transfer via ions in solution—hence the name—Solion. This is in contrast to solid-state electronics (charge transfer by electron/hole pairs in a solid conductor or semiconductor) and vacuum tubes (charge transfer by free electrons in an ionized gas or vacuum). Solion technology was first developed in the 1950s by US-Navy sponsored research. Early applications of Solion devices were for detection of low-frequency acoustic waves, either in the form of an infrasonic microphone or limited-band seismometer. Significant work on Solion motion detectors was continued in Russia, where the term Molecular Electronic Transducer (MET) was introduced to describe such a device. Inspired by the exceptionally high rate of mechanical signal conversion to electric current in MET involving mass and charge transport, pioneering MET studies provide an alternative paradigm in the development of motion sensors in wide variety of applications including nuclear explosion monitoring and seismic sensing in planetary exploration. The advantages of MET motion sensors include their small size, lack of fragile moving parts (thus high shock tolerance), high sensitivity and low noise especially at low frequencies, and independence of the response on installation angle. However, despite the rather high output parameters obtained, conventional MET devices developed and produced at present have a number of disadvantages that ultimately limit their application range. Some disadvantages include high cost of transducer manufacturing and instrument self-noise.
What is needed, therefore, is a technology capable of producing effective sensing cells at reduced cost and minimized self-noise.